How do you do a Bode plot comparison with LTSpice?

In summary: So you can do comparisons.In summary, the conversation discusses using LTSpice to fine tune LC circuits and the issue of not being able to visually compare the effects of changes due to the previous plot being overwritten. The possibility of using the Stepping function to step component values and the Monte Carlo features of the SPICE program for optimization are also mentioned as potential solutions. Another solution suggested is to put all schematics into one large schematic with different/renamed nodes to superimpose graphs.
  • #1
Landru
107
1
I'm trying to use LTSpice in order to fine tune LC circuits, but a road block I've hit is that when I run the simulation and generate a bode plot, the previous plot is overwritten, so I can't visually compare the effects of the L C changes. Some graphing programs have a function that let's you save a plot line, so that subsequent plottings can be visually seen against a previous plot. Does LTSpice have this functionality?

Thanks a lot!
 
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  • #2
Landru said:
I'm trying to use LTSpice in order to fine tune LC circuits, but a road block I've hit is that when I run the simulation and generate a bode plot, the previous plot is overwritten, so I can't visually compare the effects of the L C changes. Some graphing programs have a function that let's you save a plot line, so that subsequent plottings can be visually seen against a previous plot. Does LTSpice have this functionality?

Thanks a lot!
What are you varying between your runs? Can you use the Stepping function to step component values to get all the curves on the same plot?
 
  • #3
berkeman said:
What are you varying between your runs? Can you use the Stepping function to step component values to get all the curves on the same plot?

I change the capacitance, inductance and resistances to see how it changes the Q and the resonant peak. All that is going well, it's just that short of making screen shots, I'm not sure how to compare differences from test run to test run.

I'll looking into stepping and see if that would do it.
 
  • #4
Here's one solution I found on the 'net in case anyone comes across this in a google search:

"I have figured out an asinine way to work around this. Put all schematics into one large schematic with all different/renamed nodes. Now all graphs can be superimposed."
 
  • #5
Landru said:
Put all schematics into one large schematic with all different/renamed nodes. Now all graphs can be superimposed."
LOL. That might work for small circuits, but not for more complex ones. Unless you're running your SPICE program on a supercomputer... :smile:
 
  • #6
Yeah, works in my case. Pretty hacky though.
 
  • #7
Were you able to find the Stepping options? I use Micro-Cap, not LTSpice, so I don't know what your options are for stepping...
 
  • #8
Also, if you are trying to optimize something, look into using the Monte Carlo features of your Spice program...
 
  • #9
berkeman said:
Were you able to find the Stepping options? I use Micro-Cap, not LTSpice, so I don't know what your options are for stepping...

Yes! In some ways that's even more convenient than what I had in mind, although it's not quite as good at "quick and dirty" comparisons, since it's more like a macro and not like a simple "screen grab". Thanks for tipping me off to that feature.
 
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  • #10
There are also ways to run multiple simulations and change parameters with each sim.
 

FAQ: How do you do a Bode plot comparison with LTSpice?

1. How do I create a Bode plot in LTSpice?

To create a Bode plot in LTSpice, you will need to first simulate your circuit in the time domain. Then, go to the "View" menu and select "FFT" to see the frequency domain data. From there, you can plot the magnitude and phase of your circuit's response.

2. How do I compare multiple Bode plots in LTSpice?

To compare multiple Bode plots in LTSpice, you can use the "Add Trace" option in the FFT window. This will allow you to add additional plots to the same graph, making it easy to compare the frequency response of different circuits.

3. How can I change the frequency range of my Bode plot in LTSpice?

To change the frequency range of your Bode plot in LTSpice, you can use the "Set FFT Parameters" option in the FFT window. From there, you can adjust the start and stop frequencies, as well as the number of points in the plot.

4. Can I add labels and titles to my Bode plot in LTSpice?

Yes, you can add labels and titles to your Bode plot in LTSpice. Simply go to the "Plot Settings" menu in the FFT window and select the "Title" option. This will allow you to add a title and labels to your plot.

5. How do I save my Bode plot in LTSpice?

You can save your Bode plot in LTSpice by going to the "File" menu and selecting "Export". From there, you can choose to save the plot as an image file or a data file that can be opened in other software for further analysis.

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